This invention relates to beam-type suspension systems for wheeled vehicles. More particularly, this invention relates to certain unique axle-to-beam connections for such suspension systems.
Beam-type suspension systems for medium and heavy duty vehicles have been known for many years. Generally, in such a suspension system there is a beam which extends longitudinally and substantially parallel to the frame of the vehicle The beam is usually connected at one end to the frame of the vehicle by a hanger bracket and intermediate its ends to the axle by what may generally be referred to as a "beam-to-axle connection". In certain popular units the beam also has along its length one or more pneumatic chambers (e.g. air bags) which also connect to the frame of the vehicle, thereby to provide an "air-ride" or resilient pneumatic chamber to take up some of the articulation forces and load of the vehicle. At times the beam itself may be a resilient member such as a leaf spring.
In these suspensions further resilient members other than the air bags and/or leaf springs must be employed in order to insure the integrity of the system and to render the ride an acceptable one for the occupant and/or cargo of the vehicle. Such resilient members, however, must not be so resilient as to unacceptably reduce stability or be of such a nature a stop require frequent maintenance and repair.
In the currently known and commercially recognized suspensions of the beam type, the pivotal connection of the beam to the hanger bracket is usually resiliently bushed with an elastomeric the pivotal connection of the beam to meric material and a design decision is then made as to how, if at all, the beam-to-axle connection will be formed. In one popular unit, disclosed in U.S. Pat. No. 3,332,701, two laterally extending, resiliently bushed pins are employed. The pins extend laterally through the beam and between the opposite walls of a saddle connection which in its upper portion houses the axle. The pins may be of uniform cylindrical shape, or they may be shaped and spaced so as to provide for greater flexibility or force control in the axle attachment.
While this type of beam-to-axle connection has been quite popular, and of commercial utility, it is not without its problems. For example, it requires two longitudinal "pins" which are in fact a complex combination of tubes and other parts resulting in the need for one molded part, a bolt and three machined parts for each "pin". Various difficulties also occur with regard to the choice of spacing of the pins and metal-to-metal contact can occur during side loading such as may be experienced during cornering.
U.S. Pat. No. 4,371,190 discloses another type of resilient bushing at the axle-to-beam connection. In this device there is employed a wrap-around bushing extending under and around the beam in a saddle-like housing. While such a device overcame many of the problems of the two pin connection described above as well as previously known wrap-around connections, it requires a single offset pin to handle the axle wrap-up forces, thus adding to the cost of the system. Moreover, a complete wrapping of the beam is required to maintain the larger parts required by this system structurally rigid. In some embodiments, this complete wrapping can make the suspension unacceptably expensive and can present spacing problems.
In yet another known suspension, the axle-to-beam connection is rigid and the articulation forces of the suspension are taken up at the hanger end of the beam by specially designed or multiple bushings located between the beam and the hanger bracket. Such suspensions are disclosed in U.S. Pat. No. 4,166,640. while such suspensions have proven to be an excellent approach and certain embodiments have met with considerable commercial success, in its application it requires specialized and/or multiple tubular bushings which can increase the cost of the suspension system.
From the above, it can be seen that there is a need in the axle suspension art for a beam-to-axle connection assembly which has the common features of efficacy, inexpensiveness, involves no metal to metal contact, minimal interference with the structural integrity of the beam and uniform wearing out of bushings; while retaining the capability of being employed in most medium or heavy duty axle suspension systems as a successful equivalent or superior alternative to the above-described known devices. This invention meets this need in the axle suspension art.
Generally speaking this invention provides an axle-to-beam connection for a wheeled vehicle suspension system having an axle and a beam, wherein said beam is designed to extend longitudinally of the vehicle and to have an upper, a lower, and opposing side surfaces, said axle-to-beam connection comprising an axle connection, a beam connection and means for resiliently connecting said axle connection to said beam connection which comprises a plurality of resilient loci capable of reacting to the torsional, vertical and longitudinal loads experienced by said system, said means being of a size dependant on the motion and force occurring on the means during articulation of the suspension said loci being located proximal the side surfaces of said beam.
In certain embodiments of this invention the plurality of resilient locii varies in depth, height and width and forms a continuous, corrugated longitudinal path between the axle connection and the beam connection.
This invention can be implemented in a suspension system by providing a center of rotation, transverse to the beam and parallel to the axle, in the beam-to-axle connection at one specific point, such as a pinor a bolt. The resilient member containing the resilient loci is then designed around this center of rotation. The resilient member is located between two separate members (e.g. plates) which are separately and fixedly attached to or are a part of the beam and the axle, respectively, and through which all the forces on the beam and axle are transmitted to the resilient member so that all the vertical, lateral and torsional loads exerted on the beam-to-axle connection are concentrated in the resilient member.
Once the center of rotation is provided the resilient material is designed as a series of spaced concentric cylinders or arcual portions having the center of rotation as the center of the cylinders and arcual portions. The circular design of the resilient material is employed so that the torsional forces of the axle-to-beam connection (centered around the center of rotation) are equally distributed amongst and opposed by all the loci comprising the resilient material. The depth of the resilient member (parallel to the axle) is limited by the wheel clearance and also, in some embodiments, by the axle connection member. The thickness of the cylinders and arcual portions is chosen from well-known rubber design handbooks based on the loading which the axle-to-beam connection is designed to withstand and on the physical characteristics of the other elements of the entire axle suspension, as follows.
From the maximum loading which will be exerted on the suspension system and the physical characteristics of the other elements of the suspension system, the spring rate and amount of roll in the suspension system can be determined. The resilient member is then designed for this spring rate and amount of roll to provide for a certain maximum angle of deflection between the axle connection and the beam connection. The rubber in each concentric cylinder or arcual portion must be thick enough so that the rubber does not "pinch out" of its space during maximum deflection. This, of course, means that as the concentric cylinders and arcual portions get farther away from the center of rotation, the thicker the rubber comprising that cylinder or arcual portion must be.
After designing the system to withstand the potential torsional loading, the ability of the system to withstand the potential vertical and lateral loads must be examined by the well-known design technique of determining the "projected area" of the plurality of horizontal and the vertical planes comprising the resilient material to determine if enough rubber is provided for in these planes to withstand the projected vertical and lateral loads which the system will encounter. If the "projected areas" are not large enough, additional thickness can be added to the concentric cylinders, arcual portions or to other portions of the resilient material until enough resilient material is present to withstand the projected vertical and horizontal loads. The concentric design of the resilient material will ensure that the vertical and lateral forces exerted on the resilient material wil be uniformly exerted on the loci comprising the resilient material.
In certain embodiments of this invention, the concentric cylinders and arcual portions may be connected by resilient material so that all the cylinders, arcual portions, etc. comprise a unitary piece of resilient material. It is desirable to alternate the connecting resilient material portions between opposite ends of the concentric cylinders and arcual portions such that the resilient material assumes a corrugated shape so that more surface area of the resilient material is provided for the resilient material to be bonded to the axle and beam connection members. Among other advantages of this design, this will increase the connection's ability to withstand shear forces since the beam and axle connection members can be attached to alternating sides of the cylinders and arcual portions. The connecting resilient members need not be of any substantial thickness since the concentric circles are designed to handle the loading on the resilient member. It is therefore desirable to not bond the connecting resilient material to the beam and axle connection interfacing surfaces since as to do so would provide a weakness in the ability of the resilient material to withstand shear forces.
The resilient material is designed and shaped so that each locus takes substantially its fair share, but no more, of the torsional, vertical and longitudinal forces exerted on the resilient material, resulting in uniform wear of the resilient material.
This feature gives a maximum life to the resilient bushing, thus reducing the time between which the bushings will need to be removed and replaced. This feature also reduces the possibility of an operator driving the vehicle with part of the resilient member being worn out, this reducing the possibility of metal-to-metal contact and wear on the metal surfaces, as well as possible permanent damage to the suspension system.
Another important feature of this invention is that the structural integrity of the beam is not disturbed by the axle-to-beam connection. Small holes may have to be drilled in the beam to provide for the connection of the abutting member and to pass therethrough a means to tie the connection together (e.g. as bolt assembly), but the holes necessary for this are few and too small to affect the structural integrity of the beam. Moreover, it may be necessary to drill these holes in the sidefaces of the beam, and not in the top and bottom plates thereof.
Furthermore, this invention provides that the axle connection and the beam or beam connection do not directly abut, but are interfaced on all opposing faces by a resilient material which may be adhered in part to the axle connection on one side and the beam or beam connection on the opposite side.